The invention relates to a transportable apparatus for testing the tooth flank profile and the tooth flank lines (tooth angle) of gear wheels, in particular gear wheels of large diameter, or gear machines or tooth flank grinding machines as well as a method for positioning this apparatus and for orienting the measuring scanner at the gear teeth for the measuring operation. The apparatus includes a frame which can be leveled from the machine carriage or the workpiece table by adjusting means and can be aligned at a correct angle with respect to the gear teeth of the test object. On a first carriage movable at a tangent to the gear wheel, the apparatus frame carries a motor-driven second carriage which is movable toward and away from the gear wheel at right angles to the first carriage, and a spherical measuring scanner is movable by the second carriage for performing testing on a stationary or arrested gear wheel. The apparatus further has an orientation sensor which can be moved into various tooth gaps and has a ball at its end, corresponding to the gear wheel modulus, for ascertaining the apparatus position by means of a computer connected to the apparatus. The tangential and radial position of the orientation sensor can be transmitted to this computer via incremental travel transducers effective in travel directions, or the movement of the measuring scanner is controllable by this computer via the travel transducers.
In testing gear wheels of large diameter, transportable testing apparatuses are preferably used so that the gear wheel can be tested directly in the gear making machine and does not have to be moved to the test apparatus and secured there. Transportable testing apparatuses also have the advantage that the gear wheels can be tested on side, that is, when they are installed for use in a machine. With transportable testing apparatuses of this kind, one main probolem is that the apparatus has to be put into a definite reference position relative to the gear wheel to be tested. For it is only when the position of the apparatus relative to the gear wheel is known exactly that the scanning of the tooth flanks can provide conclusive data on any possible gearing errors and their magnitude.
The prior art already encompasses various proposals for aligning the testing apparatus with respect to the gear wheel to be tested and ascertaining its position. From German Offenlegungsschrift 29 52 497, a method and an apparatus are known in which the test apparatus is first aligned relative to the gear wheel to be tested such that the plane of adjustment of the orientation sensor is at right angles to the axis of the gear wheel. Then the orientation sensor is moved into a tooth gap until it rests on both adjacent tooth flanks of this tooth gap. The gear wheel is then rotated about its axis, carrying the orientation sensor along with it, and the displacement of the orientation sensor thereby occurring is measured; from these measurements the position of the orientation sensor or of the test apparatus relative to the gear wheel is calculated. The rotation of the gear wheel is effected such that the orientation sensor is first displaced toward the test apparatus until the tooth gap containing the sensor has attained its culmination point relative to the testing apparatus, at which the orientation sensor moves back away from the testing apparatus. This turnaround point is measured, and from it, in combination with the also-measured initial position of the orientation sensor at the beginning of the rotational movement, the position of the test apparatus relative to the gear wheel can be calculated. The coordinates are thus obtained for some selected point of the test apparatus, for instance its measuring sensor relative to a coordinate system that begins at the gear wheel axis and extends at right angles thereto.
The reversal of movement at the turnaround point of the orientation sensor can be measured only with difficulty, however. In a gear wheel two meters (m) in diameter, for instance, the wheel must be rotated by about three millimeters (mm) at its circumference before a difference in height of one micron (nm) becomes perceptible. In other words the test apparatus will be positioned incorrectly within this 3 mm, which represents an incorrect oblique position of the profile curve, which in turn simulates a pitch circle error of the profile curve; thus this apparatus can be used for positional testing only for gears of low quality.
The same problems underlie the subject of German Offenlegungsschrift 29 34 347. There, two supporting means are used which are disposed parallel to one another and are moved simultaneously into two gaps of the gear wheel to be tested. This alignment of the test apparatus is affected in the same manner as that mentioned above by possible inherent errors in the teeth and is subject to the same fundamental inaccuracies.
Finally, a method and an apparatus are known from German Offenlegungsschrift 31 25 693, which for positioning purposes uses a pivotable lever having a precision measuring ball as well as angle and length measuring systems, and furthermore for the actual testing uses a separate compound carriage having two incremental measuring systems for the X and Y directions of movement.
The disadvantage here is the positioning of the apparatus with the angle measuring system and the pivot arm, which is up to approximately 400 mm long, so that the apparatus can also be positioned on a wide base with respect to the gear wheel. The wider the base is, that is, the greater the possible pivoting angle is, the more accurate is the positioning with respect to the test object gear teeth.
The most accurate angle measuring system has an accuracy of only .+-.1.5", which given a radius of 200 mm corresponds to a measurement inaccuracy of .+-.1.5 .mu.m; and at a radius of 400 mm, which corresponds to the length of the pivoting arm, this represents an inaccuracy of .+-.1 .mu.m. This inaccuracy of the angle measuring system is correspondingly disadvantageous for the positioning of the apparatus.
This known apparatus is furthermore very expensive, because a compound carriage is additionally required for measuring the profile and tooth flank line deviations. The substantial structural size and the great weight of this known transportable apparatus are also due to this additional compound carriage.